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Numero intero de l'UnitĂ del giorno 2009-12-13, dall'archivio de l'UnitĂ .

Topics: newspapers, quotidiani, l'UnitĂ

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Sep 19, 2013
09/13

by
Neil Barnaby; Zhiqi Huang

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In a variety of inflation models the motion of the inflaton may trigger the production of some non-inflaton particles during inflation, for example via parametric resonance or a phase transition. Particle production during inflation leads to observables in the cosmological fluctuations, such as features in the primordial power spectrum and also nongaussianities. Here we focus on a prototype scenario with inflaton, \phi, and iso-inflaton, \chi, fields interacting during inflation via the...

Source: http://arxiv.org/abs/0909.0751v3

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Sep 17, 2013
09/13

by
Cristian Ion

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We study the Hilbert function and the Hilbert series of the vertex cover algebra $A(G)$, where $G$ is a Cohen-Macaulay bipartite graph.

Source: http://arxiv.org/abs/0912.2438v1

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Sep 22, 2013
09/13

by
Ryan Chornock; J. S. Bloom; S. B. Cenko; A. V. Filippenko; J. M. Silverman; M. D. Hicks; K. J. Lawrence; A. J. Mendez; M. Rafelski; A. M. Wolfe; ;

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The quasar SDSS J153636.22+044127.0, exhibiting peculiar broad emission-line profiles with multiple components, was proposed as a candidate sub-parsec binary supermassive black hole system. More recently, imaging revealed two spatially distinct sources, leading some to suggest the system to be a quasar pair separated by ~5 kpc. We present Palomar and Keck optical spectra of this system from which we identify a third velocity component to the emission lines. We argue that the system is more...

Source: http://arxiv.org/abs/0906.0849v2

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Sep 17, 2013
09/13

by
Kenji Bekki

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We propose that the rotational kinematics of the globular cluster system (GCS) in M31 can result from a past major merger event that could have formed its bulge component. We numerically investigate kinematical properties of globular clusters (GCs) in remnants of galaxy mergers between two disks with GCs in both their disk and halo components. We find that the GCS formed during major merging can show strongly rotational kinematics with the maximum rotational velocities of 140 - 170 km/s for a...

Source: http://arxiv.org/abs/0912.2476v1

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Sep 17, 2013
09/13

by
Hannes Nickisch; Pushmeet Kohli; Carsten Rother

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Many successful applications of computer vision to image or video manipulation are interactive by nature. However, parameters of such systems are often trained neglecting the user. Traditionally, interactive systems have been treated in the same manner as their fully automatic counterparts. Their performance is evaluated by computing the accuracy of their solutions under some fixed set of user interactions. This paper proposes a new evaluation and learning method which brings the user in the...

Source: http://arxiv.org/abs/0912.2492v1

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Sep 19, 2013
09/13

by
Osvaldo P. Santillan

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A method for constructing explicit Calabi-Yau metrics in six dimensions in terms of an initial hyperkahler structure is presented. The equations to solve are non linear in general, but become linear when the objects describing the metric depend on only one complex coordinate of the hyperkahler 4-dimensional space and its complex conjugated. This situation in particular gives a dual description of D6-branes wrapping a complex 1-cycle inside the hyperkahler space, which was studied by...

Source: http://arxiv.org/abs/0909.1718v4

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Sep 17, 2013
09/13

by
Siert Wieringa; Matti Niemenmaa; Keijo Heljanko

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This paper investigates approaches to parallelizing Bounded Model Checking (BMC) for shared memory environments as well as for clusters of workstations. We present a generic framework for parallelized BMC named Tarmo. Our framework can be used with any incremental SAT encoding for BMC but for the results in this paper we use only the current state-of-the-art encoding for full PLTL. Using this encoding allows us to check both safety and liveness properties, contrary to an earlier work on...

Source: http://arxiv.org/abs/0912.2552v1

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Sep 17, 2013
09/13

by
Xiaohui Liu

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A recent study indicates that the $\alpha^2\alpha_s^2$ order QED processes of $\Upsilon \to \jpsi + X$ decay are compatible with those of QCD processes. However, in the endpoint region, the Non-relativistic QED (NRQED) calculation breaks down since the collinear degrees of freedom are missing under the framework of this effective theory. In this paper we apply the soft collinear effective theory (SCET) to study the color-singlet QED process at the kinematic limit. Within this approach we are...

Source: http://arxiv.org/abs/0912.2472v1

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Sep 22, 2013
09/13

by
Junli Li; Cong-Feng Qiao

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The three photons from the dominant ortho-positronium decay and two vector mesons from the $\eta_c$ exclusive decays are found to be in tripartite and high-dimensional entangled states, respectively. These two classes of entangled states possess the Hardy type nonlocality and allow a priori for quantum mechanics vs local realism test via Bell inequalities. The experimental realizations are shown to be feasible, and a concrete scheme to fulfill the test in experiment via two-vector-meson...

Source: http://arxiv.org/abs/0812.0869v4

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Sep 19, 2013
09/13

by
Gaurav Narain; Roberto Percacci

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We discuss the arbitrariness in the choice of cutoff scheme in calculations of beta functions. We define a class of "pure" cutoff schemes, in which the cutoff is completely independent of the parameters that appear in the action. In a sense they are at the opposite extreme of the "spectrally adjusted" cutoffs, which depend on all the parameters that appear in the action. We compare the results for the beta functions of Newton's constant and of the cosmological constant...

Source: http://arxiv.org/abs/0910.5390v2

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Sep 19, 2013
09/13

by
Neil Barnaby; J. Richard Bond; Zhiqi Huang; Lev Kofman

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We study (p)reheating in modular (closed string) inflationary scenarios, with a special emphasis on Kahler moduli/Roulette models. It is usually assumed that reheating in such models occurs through perturbative decays. However, we find that there are very strong non-perturbative preheating decay channels related to the particular shape of the inflaton potential (which is highly nonlinear and has a very steep minimum). Preheating after modular inflation, proceeding through a combination of...

Source: http://arxiv.org/abs/0909.0503v2

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Sep 17, 2013
09/13

by
Hao Wang; Wendy MacCaull

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Timed model checking, the method to formally verify real-time systems, is attracting increasing attention from both the model checking community and the real-time community. Explicit-time description methods verify real-time systems using general model constructs found in standard un-timed model checkers. Lamport proposed an explicit-time description method using a clock-ticking process (Tick) to simulate the passage of time together with a group of global variables to model time requirements....

Source: http://arxiv.org/abs/0912.2553v1

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Sep 17, 2013
09/13

by
Motoaki Hirayama; Masatoshi Imada

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We propose a method to systematically control carrier densities at the interface of transition-metal oxide heterostructures without introducing disorders. By inserting non-polar layers sandwiched by polar layers, continuous carrier doping into the interface can be realized. This method enables us to control the total carrier densities per unit cell systematically up to high values of the order unity.

Source: http://arxiv.org/abs/0912.2484v1

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Sep 17, 2013
09/13

by
Keith Andrew; Karla M. Andrew; Kevin A. Andrew

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Utilizing data available from the Kentucky Geonet (KYGeonet.ky.gov) the fossil fuel mining locations created by the Kentucky Geological Survey geo-locating oil and gas wells are mapped using ESRI ArcGIS in Kentucky single plain 1602 ft projection. This data was then exported into a spreadsheet showing latitude and longitude for each point to be used for modeling at different scales to determine the fractal dimension of the set. Following the porosity and diffusivity studies of Tarafdar and Roy1...

Source: http://arxiv.org/abs/0912.2540v1

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Sep 17, 2013
09/13

by
Julianna S. Tymoczko

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Divided difference operators are degree-reducing operators on the cohomology of flag varieties that are used to compute algebraic invariants of the ring (for instance, structure constants). We identify divided difference operators on the equivariant cohomology of G/P for arbitrary partial flag varieties of arbitrary Lie type, and show how to use them in the ordinary cohomology of G/P. We provide three applications. The first shows that all Schubert classes of partial flag varieties can be...

Source: http://arxiv.org/abs/0912.2545v1

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Sep 17, 2013
09/13

by
Kate H. R. Rubin; Benjamin J. Weiner; David C. Koo; Crystal L. Martin; J. Xavier Prochaska; Alison L. Coil; Jeffrey A. Newman

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We present an analysis of the MgII 2796, 2803 and FeII 2586, 2600 absorption line profiles in coadded spectra of 468 galaxies at 0.7 < z < 1.5. The galaxy sample, drawn from the Team Keck Treasury Redshift Survey of the GOODS-N field, has a range in stellar mass (M_*) comparable to that of the sample at z~1.4 analyzed in a similar manner by Weiner et al. (2009; W09), but extends to lower redshifts and has specific star formation rates which are lower by ~0.6 dex. We identify outflows of...

Source: http://arxiv.org/abs/0912.2343v1

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Oct 24, 2014
10/14

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Shirazi, Abolfazl; Bahiraee, Amin; Ahmadi, Ebrahim; Nazari, Hassan; Heidari, Banafsheh; Borjian, Sara

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This article is from Avicenna Journal of Medical Biotechnology , volume 1 . Abstract The aim of this study was to compare the effect of time of parthenogenetic activation (22 hr versus 27 hr after In Vitro Maturation-IVM) on in vitro development of ovine oocytes using either single (Ionomycin 5 ÂµM for 5 min or Ethanol 7% for 7 min) or combined (ionomycin and ethanol with 6-DMAP 2 mM for 3 hr) activation treatments. The abattoir-derived in vitro matured activated oocytes were cultured in...

Source: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3558135

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36

Sep 17, 2013
09/13

by
Jean-Robert Belliard

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Iwasawa's classical asymptotical formula relates the orders of the $p$-parts $X_n$ of the ideal class groups along a $\ZM_p$-extension $F_\infty/F$ of a number field $F$, to Iwasawa structural invariants $\la$ and $\mu$ attached to the inverse limit $X_\infty=\limpro X_n$. It relies on "good" descent properties satisfied by $X_n$. If $F$ is abelian and $F_\infty$ is cyclotomic it is known that the $p$-parts of the orders of the global units modulo circular units $U_n/C_n$ are...

Source: http://arxiv.org/abs/0912.2528v1

The Virtual Observatories (VxOs) provide a host of services to data producers and researchers. They help data producers to describe their data in standard Space Physics Archive Search and Extract (SPASE) terms that enable scientists to understand data products from a wide range of missions. They offer search interfaces based on specified criteria that help researchers discover conjunctions, prominent events, and intervals of interest. In this talk, we show how VMO services can be used with Time...

Topics: NASA Technical Reports Server (NTRS), METADATA, DATA MANAGEMENT, THEMIS PROJECT, DATA RETRIEVAL,...

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Sep 17, 2013
09/13

by
Michael Usher

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We prove that a certain bilinear pairing (analagous to the Poincare-Lefschetz intersection pairing) between filtered sub- and quotient complexes of a Floer-type chain complex and of its "opposite complex" is always nondegenerate on homology. This implies a duality relation for the Oh-Schwarz-type spectral invariants of these complexes which (in Hamiltonian Floer theory) was established in the special case that the period map has discrete image by Entov and Polterovich. The duality...

Source: http://arxiv.org/abs/0912.2539v1

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Sep 17, 2013
09/13

by
Mark M. Meerschaert; Erkan Nane; Palaniappan Vellaisamy

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In a fractional Cauchy problem, the usual first order time derivative is replaced by a fractional derivative. The fractional derivative models time delays in a diffusion process. The order of the fractional derivative can be distributed over the unit interval, to model a mixture of delay sources. In this paper, we provide explicit strong solutions and stochastic analogues for distributed-order fractional Cauchy problems on bounded domains with Dirichlet boundary conditions. Stochastic solutions...

Source: http://arxiv.org/abs/0912.2521v1

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Sep 17, 2013
09/13

by
Jin Zhang; J. M. Bai; Liang Chen; Enwei Liang

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The observed radio-optical-X-ray spectral energy distributions (SEDs) of 22 hot spots and 45 knots in the jets of 35 active galactic nuclei are complied from literature and modeled with single-zone lepton models. It is found that the observed luminosities at 5 GHz (L_5GHz) and at 1 keV (L_1keV) are tightly correlated, and the two kinds of sources can be roughly separated with a division of L_1keV=L_5GHz. Our SED fits show that the mechanisms of the X-rays are diverse. Considering the sources at...

Source: http://arxiv.org/abs/0912.2470v1

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Sep 19, 2013
09/13

by
Joanna Mikolajewska; Yuri Balega; Karl-Heinz Hofmann; Gerd Weigelt

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We report the first resolved bispectrum speckle interferometry of the symbiotic binary CH Cyg. The measured component separation, $\rho=42 \pm 2$ mas, is consistent with the one derived from the known spectroscopic orbit and distance. In particular, our result implies a total mass of the binary of $M_{\rm t}=M_{\rm g}+M_{\rm wd}=3.7^{+3.5}_{-1.7} \rm M_{\sun}$, which is in good agreement with the value $M_{\rm t}=2.7^{+1.2}_{-0.6} \rm M_{\sun}$ derived from the spectroscopic orbit solution for...

Source: http://arxiv.org/abs/0910.5176v2

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Sep 17, 2013
09/13

by
Jean-Robert Belliard; Hassan Oukhaba

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We study the torsion subgroup of the universal ordinary distribution related to a general number field. We describe a way to control this subgroup. We apply this method to the special case of an imaginary quadratic field, and we give examples of such fields where these torsion subgroups are non-trivial.

Source: http://arxiv.org/abs/0912.2532v1

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Sep 17, 2013
09/13

by
Arvind Kumar; Amruta Mishra

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We study the in-medium properties of $D$ and $\bar{D}$ mesons in isospin-asymmetric nuclear matter at finite temperatures using an effective chiral SU(4) model. The interactions of $D$ and $\bar{D}$ mesons with nucleons, scalar isoscalar meson $\sigma$, and scalar iso-vector meson $\delta$ are taken into consideration. It is found that as compared to the $\bar{D}$ mesons, the properties of the $D$ mesons are observed to be quite sensitive to the isospin-asymmetry at high densities. At finite...

Source: http://arxiv.org/abs/0912.2477v1

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Sep 17, 2013
09/13

by
Doris Folini; Rolf Walder; Jean M. Favre

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Shock bound interaction zones (SBIZs) are ubiquitous in astrophysics. We present numerical results for 2D and 3D, plane-parallel, infinitely extended SBIZs. Isothermal settings and parameterized cooling are considered. We highlight and compare characteristic of such zones. We emphasize the mutual coupling between the turbulence within the SBIZ and the confining shocks, point out potential differences to 3D periodic box studies of supersonic turbulence, and contemplate on possible effects on the...

Source: http://arxiv.org/abs/0912.2496v1

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Sep 17, 2013
09/13

by
Flera G. Kopylova; Alexander I. Kopylov

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We analyze the properties of the clusters of galaxies in the region of the Ursa Major (UMa) supercluster using observational data from SDSS and 2MASS catalogs. The region studied includes a supercluster (with a galaxy and cluster overdensity of 3 and 15, respectively) and field clusters inside the 150 Mpc diameter surrounding region. The total dynamical mass of 10 clusters of galaxies in UMa is equal to 2.25 10^15 M_sun, and the mass of 11 clusters of galaxies in the UMa neighborhood is equal...

Source: http://arxiv.org/abs/0912.2503v1

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Sep 17, 2013
09/13

by
Edwin Hobi Jr.; Renato B. Pontes; A. Fazzio; Antonio J. R. da Silva

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The formation of one-dimensional carbon chains from graphene nanoribbons is investigated using it ab initio molecular dynamics. We show under what conditions it is possible to obtain a linear atomic chain via pulling of the graphene nanoribbons. The presence of dimers composed of two-coordinated carbon atoms at the edge of the ribbons is necessary for the formation of the linear chains, otherwise there is simply the full rupture of the structure. The presence of Stone-Wales defects close to...

Source: http://arxiv.org/abs/0912.2502v1

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Sep 19, 2013
09/13

by
P. Mukherjee

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Soliton modes in a gauged sigma model with interpolating potential have been investigated. Numerical solutions using a fourth order Runge -- Kutta method are discussed. By tuning the interpolation parameter the transition from symmetrybreaking to the symmetric phase is highlighted.

Source: http://arxiv.org/abs/hep-th/9911006v3

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Sep 19, 2013
09/13

by
T. M. Wright; A. S. Bradley; R. J. Ballagh

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We perform finite-temperature dynamical simulations of the arrest of a rotating Bose-Einstein condensate by a fixed trap anisotropy, using a Hamiltonian classical-field method. We consider a quasi-two-dimensional condensate containing a single vortex in equilibrium with a rotating thermal cloud. Introducing an elliptical deformation of the trapping potential leads to the loss of angular momentum from the system. We identify the condensate and the complementary thermal component of the...

Source: http://arxiv.org/abs/0909.1683v2

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Sep 23, 2013
09/13

by
Michael Usher

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We assign to each nondegenerate Hamiltonian on a closed symplectic manifold a Floer-theoretic quantity called its "boundary depth," and establish basic results about how the boundary depths of different Hamiltonians are related. As applications, we prove that certain Hamiltonian symplectomorphisms supported in displaceable subsets have infinitely many nontrivial geometrically distinct periodic points, and we also significantly expand the class of coisotropic submanifolds which are...

Source: http://arxiv.org/abs/0903.0903v2

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Sep 17, 2013
09/13

by
Attila KertĂ©sz; Zsolt NĂ©meth

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Coordination in distributed environments, like Grids, involves selecting the most appropriate services, resources or compositions to carry out the planned activities. Such functionalities appear at various levels of the infrastructure and in various means forming a blurry domain, where it is hard to see how the participating components are related and what their relevant properties are. In this paper we focus on a subset of these problems: resource brokering in Grid middleware. This paper aims...

Source: http://arxiv.org/abs/0912.2549v1

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Sep 17, 2013
09/13

by
Bakir Farhi

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In this paper, we prove the following result: {quote} Let $\A$ be an infinite set of positive integers. For all positive integer $n$, let $\tau_n$ denote the smallest element of $\A$ which does not divide $n$. Then we have $$\lim_{N \to + \infty} \frac{1}{N} \sum_{n = 1}^{N} \tau_n = \sum_{n = 0}^{\infty} \frac{1}{\lcm\{a \in \A | a \leq n\}} .$${quote} In the two particular cases when $\A$ is the set of all positive integers and when $\A$ is the set of the prime numbers, we give a more precise...

Source: http://arxiv.org/abs/0912.2508v1

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Sep 17, 2013
09/13

by
K. G. Libbrecht; H. M. Arnold

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We present experiments investigating the growth of ice crystals from water vapor in air using a free-fall convection chamber. We measured growth rates at temperatures of -5 C and -10 C as a function of supersaturation at an air pressure near one bar. We compared our data with numerical models of diffusion-limited growth based on cellular automata to extract surface growth parameters at different temperatures and supersaturations. From these investigations we hope to better understand the...

Source: http://arxiv.org/abs/0912.2518v1

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Sep 17, 2013
09/13

by
Swastik Bhattacharya; Rituparno Goswami; Pankaj S. Joshi

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We study here the evolution of a massless scalar field in a spacetime, developing from a regular initial spacelike surface. The Einstein equations and regularity and boundary conditions governing the same are specified. Both homogeneous and inhomogeneous collapse models are considered and we analyze when the occurrence of singularity will be simultaneous or otherwise. In the inhomogeneous collapse case, we characterize a wide family of black hole solutions arising in scalar field collapse. We...

Source: http://arxiv.org/abs/0807.1985v2

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Sep 17, 2013
09/13

by
Qun Wang

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A pedagogical introduction to color superconductivity in the weak coupling limit is given. The focus is on the basic tools of thermal field theory necessary to compute observables of color superconductivity. The rich symmetry structure and symmetry breaking patterns are analyzed on the basis of the Anderson-Higgs mechanism. Some techniques can also be applied for computing neutrino processes in compact stars. As an example, we show how to obtain the neutrino emissivity for Urca processes in...

Source: http://arxiv.org/abs/0912.2485v1

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Sep 17, 2013
09/13

by
Gaston Giribet

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We consider Alday-Gaiotto-Tachikawa (AGT) realization of the Nekrasov partition function of N=2 SCFT. We focus our attention on the SU(2) theory with N_f=4 flavor symmetry, whose partition function, according to AGT, is given by the Liouville four-point function on the sphere. The gauge theory with N_f=4 is known to exhibit SO(8) symmetry. We explain how the Weyl symmetry transformations of SO(8) flavor symmetry are realized in the Liouville theory picture. This is associated to functional...

Source: http://arxiv.org/abs/0912.1930v2

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Sep 17, 2013
09/13

by
Moshe Mishali; Yonina C. Eldar; Oleg Dounaevsky; Eli Shoshan

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We present a sub-Nyquist analog-to-digital converter of wideband inputs. Our circuit realizes the recently proposed modulated wideband converter, which is a flexible platform for sampling signals according to their actual bandwidth occupation. The theoretical work enables, for example, a sub-Nyquist wideband receiver, which has no prior information on the transmitter carrier positions. Our design supports input signals with 2 GHz Nyquist rate and 120 MHz spectrum occupancy, with arbitrary...

Source: http://arxiv.org/abs/0912.2495v1

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Sep 17, 2013
09/13

by
R. Rovatti; C. Passerini; G. Mazzini

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The paper introduces a modified version of the classical Coupon Collector's Problem entailing exchanges and cooperation between multiple players. Results of the development show that, within a proper Markov framework, the complexity of the Cooperative Multiplayer Coupon Collectors' Problem can be attacked with an eye to the modeling of resource harvesting and sharing within the context of Next Generation Network. The cost of cooperation is computed in terms of exchange protocol burden and found...

Source: http://arxiv.org/abs/0912.2523v1

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Sep 22, 2013
09/13

by
M. L. Kleptsyna; A. Le Breton; M. Viot

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The explicit solution of the discrete time filtering problems with exponential criteria for a general Gaussian signal is obtained through an approach based on a conditional Cameron-Martin type formula. This key formula is derived for conditional expectations of exponentials of some quadratic forms of Gaussian sequences. The formula involves conditional expectations and conditional covariances in some auxiliary optimal risk-neutral filtering problem which is used in the proof. Closed form...

Source: http://arxiv.org/abs/0908.2960v2

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Sep 17, 2013
09/13

by
Roberto Tauraso

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We determine the explicit formulas for the sum of products of homogeneous multiple harmonic sums $\sum_{k=1}^n \prod_{j=1}^r H_k(\{1\}^{\lambda_j})$ when $\sum_{j=1}^r \lambda_j\leq 5$. We apply these identities to the study of two congruences modulo a power of a prime.

Source: http://arxiv.org/abs/0912.2497v1

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Sep 19, 2013
09/13

by
Lucas Vienne

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Let n >1 be an integer, and G a doubly transitive subgroup of the symmetric group on X={1,...,n}. In this paper we find all linear group representations rho of G on an euclidean vector space V which contains a set of equiangular vector lines GG={ < v_1>,...,} such that : (1) V is generated by v_1,...,v_n, (2) for all i in X and all g in G, = . Then we illustrate our construction when G=SL_d(q), q odd and d > 1.

Source: http://arxiv.org/abs/0910.1655v2

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Sep 17, 2013
09/13

by
J. Smyrnakis; M. Magiropoulos; G. M. Kavoulakis; A. D. Jackson

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A two-component Bose-Einstein condensate that is confined in a one-dimensional ring potential supports solitary-wave solutions, which we evaluate analytically. The derived solutions are shown to be unique. The corresponding dispersion relation that generalizes the case of a single-component system shows interesting features.

Source: http://arxiv.org/abs/0912.2483v1

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Sep 22, 2013
09/13

by
Kevin Buchin

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We present a new and simple randomized algorithm for constructing the Delaunay triangulation using nearest neighbor graphs for point location. Under suitable assumptions, it runs in linear expected time for points in the plane with polynomially bounded spread, i.e., if the ratio between the largest and smallest pointwise distance is polynomially bounded. This also holds for point sets with bounded spread in higher dimensions as long as the expected complexity of the Delaunay triangulation of a...

Source: http://arxiv.org/abs/0812.0387v3

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Sep 17, 2013
09/13

by
Koji Ishiwata; Shigeki Matsumoto; Takeo Moroi

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Motivated by the PAMELA anomaly in the fluxes of cosmic-ray positron and electron, we study the cosmic gamma-ray induced by the inverse Compton (IC) scattering process in unstable dark matter scenario assuming that the anomaly is due to the positron and electron emission by the decay of dark matter. We calculate the fluxes of IC-induced gamma-ray produced in our Galaxy and that from cosmological distance, and show that both of them are significant. We discuss a possibility that large dark...

Source: http://arxiv.org/abs/0912.2486v1

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Sep 23, 2013
09/13

by
Agelos Georgakopoulos

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Let $G$ be a graph each edge $e$ of which is given a length $\ell(e)$. This naturally induces a distance $d_\ell(x,y)$ between any two vertices $x,y$, and we let $\ell-TOP$ denote the completion of the corresponding metric space. It turns out that several well studied topologies on infinite graphs are special cases of $\ell-TOP$. Moreover, it seems that $\ell-TOP$ is the right setting for studying various problems. The aim of this paper is to introduce $\ell-TOP$, providing basic facts,...

Source: http://arxiv.org/abs/0903.1744v3

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42

Sep 22, 2013
09/13

by
Christopher Gaul; Nina Renner; Cord A. Mueller

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Disorder modifies the sound-wave excitation spectrum of Bose-Einstein condensates. We consider the classical hydrodynamic limit, where the disorder correlation length is much longer than the condensate healing length. By perturbation theory, we compute the phonon lifetime and correction to the speed of sound. This correction is found to be negative in all dimensions, with universal asymptotics for smooth correlations. Considering in detail optical speckle potentials, we find a quite rich...

Source: http://arxiv.org/abs/0908.1947v2

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Sep 17, 2013
09/13

by
JP Furness; PA Crowther; PW Morris; CL Barbosa; RD Blum; PS Conti; SD van Dyk

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We present near-IR VLT/ISAAC and mid-IR Spitzer/IRS spectroscopy of the young massive cluster in the W31 star-forming region. H-band spectroscopy provides refined classifications for four cluster members O stars with respect to Blum et al. In addition, photospheric features are detected in the massive Young Stellar Object (mYSO) #26. Spectroscopy permits estimates of stellar temperatures and masses, from which a cluster age of ~0.6 Myr and distance of 3.3 kpc are obtained, in excellent...

Source: http://arxiv.org/abs/0912.2544v1

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45

Sep 17, 2013
09/13

by
Stefan Blom; Jaco van de Pol

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We present a new distributed algorithm for state space minimization modulo branching bisimulation. Like its predecessor it uses signatures for refinement, but the refinement process and the signatures have been optimized to exploit the fact that the input graph contains no tau-loops. The optimization in the refinement process is meant to reduce both the number of iterations needed and the memory requirements. In the former case we cannot prove that there is an improvement, but our experiments...

Source: http://arxiv.org/abs/0912.2550v1